Method and apparatus for electrical stimulation of the gastrointestinal tract

ABSTRACT

A method and apparatus for providing electrical stimulation of the gastrointestinal tract. The apparatus features an implantable pulse generator which may be coupled to the gastric system through one or more medical electrical leads. In the preferred embodiment the leads couple to the circular layer of the stomach. The pulse generator preferably features sensors for sensing gastric electrical activity, and in particular, whether peristaltic contractions are occurring. In particular two sensors are featured. The first sensor senses low frequency gastrointestinal electrical activity between the frequency of 0.017-0.25 Hz and the second sensor senses intrinsic gastrointestinal electrical activity between the frequency of 100-300 Hz, which occurs upon normal peristaltic contractions. The second sensor only senses for a preset period after low frequency gastrointestinal electrical activity has been sensed by the first sensor. The pulse generator further delivers stimulation pulse trains to the gastrointestinal tract at a period of time after low frequency gastrointestinal electrical activity has been sensed by the first sensor. If, however, the second sensor senses intrinsic gastrointestinal electrical activity between the frequency of 100-300 Hz, then the delivery of stimulation pulse trains to the gastrointestinal tract is inhibited. In such a manner the present invention detects the occurrence of normal peristaltic contractions and further provides electrical stimulation to the gastrointestinal tract if such normal peristaltic contractions are not detected.

FIELD OF THE INVENTION

The invention relates to treatment of gastrointestinal disorders using amethod and apparatus for providing electrical stimulation of thegastrointestinal tract.

BACKGROUND OF THE INVENTION

The gastrointestinal tract is responsible for an essential step in thedigestive process, the reception of nutrition in the human body. Animportant element of the digestive process is peristalsis, thecoordinated and self-regulated motor activity of the intestinal tract.Peristalsis is accomplished through a coordinated combination ofelectrical, chemical, neurological and hormonal mediation, as well aspossibly other, as yet unknown, mechanisms.

Many diseases and maladies can affect the motor activity of thegastrointestinal tract, causing malfunction of the digestive process.Such diseases include diabetes mellitus, scleroderma, intestinalpseudo-obstruction, ileus, and gastroparesis.

Gastroparesis, for example, is a chronic gastric motility disorder inwhich there is delayed gastric emptying of solids and/or liquids.Symptoms of gastroparesis may range from early satiety and nausea inmild cases to chronic vomiting, dehydration, and nutritional compromisein severe cases. Diagnosis of gastroparesis is based on demonstration ofdelayed gastric emptying of a radio-labeled solid meal in the absence ofmechanical obstruction. Gastroparesis may occur for a number of reasons.Approximately one third of patients with gastroparesis, however, have noidentifiable underlying cause (often called idiopathic gastroparesis).Management of gastroparesis involves four areas: (1) prokinetic drugs,(2) antiemetic drugs, (3) nutritional support, and (4) surgical therapy(in a very small subset of patients.) Gastroparesis is often a chronic,relapsing condition; 80% of patients require maintenance antiemetic andprokinetic therapy and 20% require long-term nutritionalsupplementation. Other maladies such as tachygastria or bradygastria canalso hinder coordinated muscular motor activity of the gastrointestinaltract, possibly resulting in either stasis or nausea or vomiting or acombination thereof.

The undesired effect of these conditions is a reduced ability orcomplete failure to efficiently propel intestinal contents down thedigestive tract. This results in malassimilation of liquid or food bythe absorbing mucosa of the intestinal tract. If this condition is notcorrected, malnutrition or even starvation may occur. Moreover nausea orvomiting or both may also occur. Whereas some of these disease statescan be corrected by medication or by simple surgery, in most casestreatment with drugs is not adequately effective, and surgery often hasintolerable physiologic effects on the body.

Presently, however, there is no practically effective device or systemto stimulator intelligently alter the muscular contractions of smoothmuscle and the gastrointestinal tract in particular. Therefore, there isa need in the art for a system and method to properly stimulate thegastrointestinal tract to thereby treat ineffective or absent electricalmuscular activity of the gastrointestinal tract.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a method and apparatus fortreating patients having dysfunctional gastrointestinal muscle ordisorders of smooth muscles elsewhere in the body.

This and other objects are provided by one or more of the embodimentsdescribed below. The present invention is a method and apparatus forproviding electrical stimulation of the gastrointestinal tract. Theapparatus features an implantable pulse generator which may be coupledto the gastric system through one or more medical electrical leads. Inthe preferred embodiment the leads couple to the circular layer of thestomach. The pulse generator preferably features sensors for sensinggastric electrical activity, and in particular, whether peristalticcontractions as occurring. In particular two sensors are featured. Thefirst sensor senses low frequency gastrointestinal electrical activitybetween the frequency of approximately 0.005 Hz-5 Hz ("slow waves") andthe second sensor senses intrinsic gastrointestinal electrical activitybetween the frequency of approximately 100-5000 Hz ("spike activity")which occurs upon normal peristaltic contractions and immediatelyfollows a slow wave. The second sensor only senses for a preset periodafter a slow waves has been sensed by the first sensor. The pulsegenerator further delivers stimulation pulse trains to thegastrointestinal tract at a period of time after slow waves have beensensed by the first sensor. If, however, the second sensor senses asufficient amount of spike activity, then the delivery of stimulationpulse trains to the gastrointestinal tract is inhibited. In such amanner the present invention detects the occurrence of normalperistaltic contractions and further provides electrical stimulation tothe gastrointestinal tract if such normal peristaltic contractions arenot detected.

BRIEF DESCRIPTION OF THE DRAWINGS

The above-described and other aspects of the present invention may bebetter understood and appreciated with reference to a detaileddescription of a specific embodiment of the invention, when read inconjunction with the accompanying drawings, wherein:

FIG. 1 depicts the apparatus implanted within a patient.

FIG. 2 depicts a detailed view of the stomach muscle showing theelectrode of the lead implanted.

FIG. 3 depicts a plan view of a lead used with the apparatus.

FIG. 4 is a functional block diagram of the pulse generator.

FIG. 5 is an electrogastrogram of the gastrointestinal system.

FIG. 6 is an electrogastrogram illustrating an arrhythmia and theresponse of the apparatus.

FIG. 7 is a flowchart depicting the operation of the system.

FIG. 8a-8e depict various pulse trains which may be emitted by thepresent system.

FIG. 9 depicts the steps used in the present invention to determinecontraction or vomiting or other changes in the stomach usingplethysmography.

FIG. 10 depicts the electrical stimulation delivered in the normal modeof the device.

The FIGS. are not necessarily to scale.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a system 1 implanted in a patient 2. As seen, the system 1comprises an implantable pulse generator 3 featuring two sets of leads4, 5 which are coupled to the stomach 10. The first set of leads 4provide stimulation to the stomach. The second set of leads 5 providesensing of the gastroelectrical activity of the stomach 10 to the pulsegenerator 3. In the preferred embodiment, the pulse generator 3 isimplanted within the patient 2. As such, the implantable pulse generator3 features a hermetic enclosure, as is well known in the art. The leadsused for both the first set 4 and the second set 5 may be any acceptablelead. In the preferred embodiment, the preferred leads are MedtronicModel No. 4300 intramuscular lead. Of course, other configurations ofleads or lead systems may be used, including the use of from only asingle lead, a single set of leads (i.e. two), or even the use of threeor more sets of leads. Moreover, although shown as being coupled to thestomach it must be understood the present invention may be used along oron any of the other structures and organs along the gastrointestinaltract, including the colon, small intestine, stomach or even theesophagus.

The first set of leads 4 are stimulation leads which conduct stimulationpulses from the pulse generator 3 to the stomach 10. First set of leads4 are preferably implanted through the serosa at the area within thetransition of the corpus and the antrum on the great curvature. Ofcourse, other locations for first set of leads 4 may be used, such as inthe fundus, caudud corpus as well as the orad or terminal antrum. Thesecond set of leads 5 are sensing leads which conduct anygastroelectrical activities sensed in the stomach 10 to the pulsegenerator 3. Preferably the second set of leads 5 are positioneddistally in the mid antrum also along the great curvature, althoughthese leads may also be positioned in other locations.

FIG. 2 details the preferred positioning of an electrode of a leadwithin the various layers of the stomach. As seen, the stomach 10 hasessentially seven layers of tissue. In the preferred embodiment, theelectrode of each lead is positioned into the layers of the stomachmuscle as shown. That is, the electrode is positioned such that itintersects both the longitudinal and circular layers. This is believedimportant by the inventor because in such a manner the electrode is ableto also intersect the enteric nervous system of the stomach and be inclose contact with the cells of Cajal. This is believed important asresearch has shown that intramuscular electrodes may effectivelystimulate the stomach with less than one one-thousandths of the energyrequired for serosal electrodes. Of course, other types of electrodes orlead systems may be used, including those which contact only any one ofeach of the layers of the stomach organ, such as only the mucosa or onlythe serosa. Moreover, although in the preferred embodiment a pair ofunipolar leads are used for stimulation and a second pair of unipolarleads are used for stimulation, other configurations of leads may beused, such as bipolar, tripolar, quadrapolar, as well as any otherconfiguration suitable such as a unipolar lead and can.

FIG. 3 depicts a plan view of the preferred embodiment lead 15 used inthe present invention. As seen, the lead 15 essentially has threesections, connector section 16, body section 17 and fixation section 18.Connector section 16 includes a connector pin 22 to electrically couplethe lead 15 into the pulse generator. Any connector pin 22 as well knownin the art may be used. Body section 17 includes an electrical conductor19 surrounded by an electrical insulator 20. In the preferred embodimentelectrical conductor 19 is a platinum iridium alloy and electricalinsulator 18 is silicone. Of course, other biocompatible materials mayalso be used. As seen, at the distal end of the body section 17 is anelectrode 25. In the preferred embodiment, electrode 25 is a polishedplatinum iridium alloy. Of course, other materials may likewise be used,such as a porous platinized structure. In addition, the electrode 25could further feature various pharmaceutical agents, such asdexamethasone sodium phosphate or beclomethasone phosphate in order tominimize the inflammatory response of the tissue to the implanted lead15. Other agents such as antibiotics may also be used. Located distal tothe electrode 25 is the fixation section 18. As seen, fixation section18 has essentially two piece parts, a suture 26 which is in turn coupledto a needle 27. Needle 27 is preferably curved. In an alternateembodiment suture may feature a fixation coil as is well known in theart to cooperate with the body tissue after implantation to maintain thelead 15 in the position implanted. Of course, other fixation mechanismsmay be used, such as fixation discs, as is well known in the art.

FIG. 4 depicts a functional block diagram of the gastrointestinal pulsegenerator according to the present invention. As seen, pulse generator 3is enclosed by hermetic enclosure 40 to the electronics and batterywhile the device is implanted. Hermetic enclosure may consist of anysuitable construction. Pulse generator 3 couples with two sets of leads4, 5 which are, in turn, coupled to the stomach 10. The first set ofleads 4 transmits stimulation pulses from pulse generator 3 to thestomach. The second set of leads 5 provide sensing of thegastroelectrical activity of the stomach 10 to the pulse generator 3.Although in the preferred embodiment the stimulating leads and sensingleads are separate leads, the present invention may also be employedusing a combination of lead which both sense and stimulate.

As seen, the sensing leads 4 are coupled into a slow wave detectioncircuit 41. Slow wave detection circuit 41 includes a band passamplifier, a slew rate converter and two threshold detectors.Essentially, such a slow wave detection circuit 41 is similar to thoseused in a cardiac pacemaker but with several important characteristics.First, the band pass amplifier has a much lower center frequency,preferably on the order of 0.3 HZ when used in the stomach. Of course,the present invention may be used in each of the various organs alongthe GI tract so that the center frequency may be varied accordingly. Theslew rate converter operates in a manner well known in the art andgenerates a signal corresponding to the slew rate of the sensedelectrogastrogram. The threshold detectors operates in a manner wellknown in the art and generate output signals when the sensed inputsignal is above a threshold level. One threshold detector corresponds tothe peak to peak amplitude of the sensed electrogastrogram. The secondthreshold detector corresponds to the sensed slew rate.

Preferably, the slow wave detection circuit 41 must be able to detectinput signals between approximately 30 microvolts and 10 millivoltswhich have a slew rate between 100 microvolts per/second up to 10 voltsper/second with a typical value of 100 millivolts per second. Such arange may be achieved using multiple steps which are controlled by themicroprocessor 46 via the input line 46b-41d. To detect the slow wave,both threshold detectors should be coupled using a logical ANDconfiguration. Thus, a signal should then be sent via the output line41c-46a to the microprocessor 46. The slew rate detector may alsoinclude an interference detector specially designed to detect continuousinterference, especially at any of the various mains frequencies ofpower distribution (e.g. 16-400 Hz) so that false sensing is avoided. Inan alternative embodiment a second sense amplifier may be providedhaving a bandpass in the range of expected power field variations invarious frequencies of power distribution(e.g. 16-400 Hz). At everycycle the presence of interference is detected. The time intervalbetween two detections is measured and if this time interval correspondsto any of the main frequencies of power distribution which ispreprogrammed, then this detection is labeled as interference and thedetection on the other amplifier will be simultaneously labeled also asinterference detection and not as a valid slow wave.

The band pass amplifier in the detection circuit 41 should be blankedfor a period after a sensed event has been received by themicroprocessor 46 or just before and during a stimulation pulse isemitted by output stage discussed below. Blanking may be accomplishedthrough either a blanking switch which disconnects the amplifier fromthe electrodes or through a program performed in the microprocessor. Themicroprocessor 46 should also ignore sensed output signals during aperiod after a sensed or paced event. This is similar to a blankingcircuit where sensed events during a blanking period do not affect thetiming of the pulse generator. In the preferred embodiment, the blankingperiod for slow wave detection is on the order of between 0.5 to 4.0seconds.

Generally speaking, the blanking period decreases with increasing slowwave frequency. The blanking period algorithm is controlled by themicroprocessor. The blanking period algorithm operates such that whenthe slow wave interval is shortened the blanking period is alsoshortened. This shortening may be performed in any manner, for example,in a linear fashion or in some other more complex monotonous fashion.After the blanking period, during a certain timing window, themicroprocessor 46 is able to receive slow wave detection signals, whichwill not restart the pulse generator timing circuit, but will instead beinterpreted as interference by the microprocessor 46. This timingwindow, interference detection timing window, may be up to seven secondsin duration after the sensed or paced event, preferably it is 100milliseconds. To be precise, the combined blanking period andinterference detection windows are shortened. Shortening may occur inany manner desired, i.e. in a linear fashion between a preset high or apreset low value or along a non-linear manner. The shortening of thecombined blanking and interference detection interval will not occuronce the combined blanking and interference detection window reaches aprogrammed value, such as 2.5 s. This combined blanking window may alsobe programmed to be turned off such that it does not change in responseto sensed physiologic signals. In all circumstances, however, theinterference detection window remains equal to at least 100 ms. Forexample, the rationale is that the typical main frequencies of powerdistribution are 50 Hz, 60 Hz, 400 Hz and 16.33 Hz. The lower harmonicfor 1633 Hz is 8 Hz which corresponds to an interval of 125 ms. Ofcourse the exact length of time for each period may be programmed by thephysician. Moreover, each of the periods may be further made to beautomatically adjusted based on the sensed electrical activity.

As seen in FIG. 4, blanking switch 42 couples sensing electrodes 4 toamplifier 45 to detect high frequency spike activity. The operation ofblanking switch 42 causes the amplifier 45 to be connected to thesensing electrodes 4 once an intrinsic deflection or slow wave has beendetected by slow wave detection circuit 41 or a stimulus has beenemitted by output stage 47. Preferably, this occurs after a short delay.Blanking switch 42 is closed between 0.5 to 2 seconds after these eventsand opens roughly 5 to 7 seconds later or at approximately 30% of theintrinsic event interval. As seen, the switch is controlled via the line46e-42e.

The detection circuit for the high frequency spike activity detectorconsists of a bandpass amplifier having the center frequency atapproximately 300 Hz. As discussed above, however, the center frequencywill vary for different organs. The amplifier is followed by twothreshold detectors, the first detector detects peak to peak amplitudewhile the second detector detects slew rate. Both detectors are coupledusing a logical AND configuration. The detector pulses are counted, andthe interval between pulses is measured. If the interval corresponds tothe intervals of the mains frequencies of power distribution or any oftheir harmonies, i.e. 20 ms or 10 ms, they are rejected. If the numberof pulses exceeds a pre-programmed value, then a contraction isindicated. The counter is provided to store in the memory the time ofoccurrence of the contraction. The number of pulses corresponding toeach contraction may be counted and tallied to determine the strength ofthe contractions. In the present embodiment 3-5 pulses correspond to aweak contraction; 6-8 pulses correspond to a moderate contraction; 9 ormore pulses correspond to a strong contraction. Each of these values, ofcourse, may be programmed and the exact number of pulses will vary dueto the implementation.

Also coupled to the sensing electrodes 4 is an AC current generator 43.This AC current generator 43 is part of a plethysmography circuit.Overall, the plethysmography circuit is present to provide a means forsensing mechanical activity of the underlying tissue. That is, whereasthe spike activity in the electrogastrogram may be used to sensecontraction, the contraction may also be sensed using theplethysmography circuit. Plethysmography circuit is comprised from ACcurrent generator 43, amplifier, modulator and ADC converter 44 as wellas a portion of the microprocessor 46. The AC current generator 43 isswitched on via signal from microprocessor 46 once a slow wave isdetected or a pacing stimulus is emitted. It is switched off roughly 10seconds after being switched on also from the same line or signal fromthe microprocessor 46. The AC current generator 43 amplitude andfrequency are programmable via microprocessor 46. The frequency shouldbe such it is not detected by amplifiers 41, 45, e.g., 1 kHz. Ifsynchronous detection by amplifier 41 occurs at the end of the blankingperiod, then the amplitude and/or the frequency of the AC currentgenerator 43 is adjusted by the microprocessor 46 to avoid subsequentdetection of the generated AC current.

Turning now to the amplifier, the modulator and ADC converter 44, the ACvoltage caused by the injection of AC current generator 43 is amplifiedand demodulated and converted in order to detect impedance changescaused by contractions of the underlying tissue. The ADC converterdigitizes the amplitude of the demodulated signal. The digitized signalis transmitted via line 44c-46h to the microprocessor 46. Themicroprocessor 46 analyzes the signal pattern by comparing it with oneor more templates to identify it as a contraction as well as to rejectinterference or signals generated by postural changes or vomiting. Thistemplate comparison is done synchronously to the detection of the slowwave. Line 46i-44d is used to control the amplifier and ADC from themicroprocessor 46.

The microprocessor 46 handles all timings and data storage of the pulsegenerator and may be of any suitable design. In the preferredembodiment, a microprocessor 46 such as that used in the Thera I seriesof Medtronic pacemakers is used. The description of the microprocessor46 function is described in the section below which details theoperation of the algorithm used in the present invention.

Stimulation pulses are generated by the output stage 47. In thepreferred embodiment, the output stage 47 generates pulse trains. Itshould be understood many types of pulse trains or stimulation pulsesmay be used including constant current or constant voltage outputs, or amixture of both. The output pulses are transported to thegastrointestinal tissue via medical electrical leads 5 and thus to thestomach.

Turning again to the output stage 47, when an output pulse is to bedelivered, its amplitude, pulse width and duration and frequencies arecontrolled via lines 46j-47a. If it is a burst of stimuli, the frequencyand duration are controlled through the same line while a burst finishedsignal is sent to the microprocessor 46 via output line 47b-46k.

Programmability to the pulse generator 3 is achieved throughreceiver-demodulator 48 and transmitter 49. As seen, each of thesedevices is coupled to the microprocessor 46. The receiver-demodulator 48and transmitter 49 are similar to those used in cardiac pacemakers.

The basic parameter settings such as sensitivity (peak voltage or slewrate), refractory, blanking, output pulse amplitude, pulse width, escapeinterval and ratio, escape interval to a stimulation interval, arestored in the memory of the microprocessor 46. Default values are alsostored. These values can be read from memory and sent to a receiver viathe transmitter.

FIG. 5 shows an electrogastrogram of the stomach in a human. As seen,this intrinsic gastroelectric activity has two distinct components. Thefirst component 501 is a low-frequency, rhythmic depolarization termedslow waves. Superimposed on the slow wave is a high frequency spikeactivity 502 which corresponds to mechanical contractions of the organ.In the human stomach slow waves are regular, omnipresent depolarizationsat 3 cycles/min. (0.05 Hz) that commence high on the greater curvatureof the stomach, in the region referred to as the pacemaker region, andpropagate aborally, as depicted in FIG. 2.

The normal frequency range for the slow wave in the stomach is between2.7-3.4 bpm. In clinical situations this value may vary anywhere between1-15 bpm. High frequency slow wave activity (called tachygastria) doesnot permit contraction of the stomach readily and may even results in agastroparesis. In the presence of excessively slow or even absent slowwaves (called bradygastria) motility is reduced.

Slow waves and the corresponding spike activity may become irregular oruncoupled or both, thereby preventing the appearance or organization ofregular, normally propagated contractions that constitute normalmotility. Contractions cannot occur without gastric electrical responseactivity which is in turn regulated by the electrical control activity.Any disruption in this delicate sequential order may lead to delayedgastric emptying. An example of such an occurrence is shown in complex505.

The spike activity occurs incidentally for a few of the slow waves whilethe patient is in a fasting or non-eating condition. This is termedMigratory Motor Complex phase I. Immediately prior to a meal, typically30 mins, MMC I changes into MMC II. During this phase the number of slowwaves having spike activity increases. Once the meal or eating has begunand up to 120 mins after the meal each further slow wave also has aspike activity component. This condition is called MMC III.

As seen in this complex a slow wave 510 occurs which is not followed byany high frequency spike activity. The absence of such activityindicates there is no longer any peristaltic contraction which willoccur, i.e. gastric emptying is delayed.

FIG. 6 depicts electrogastrogram tracings of a stomach illustrating theoperation of the device to treat abnormal electrogastric activity. Asseen, the stomach typically has periodic slow waves which occur at anintrinsic rate of 3 beats per minute or approximately 20 seconds apart.These intrinsic slow waves typically occur at a relatively fixed rate.Here, these fixed, periodic slow waves are shown as waves 601, 602 and,603. In a normal electrogastrogram taken during a meal, each slow wavefeatures a high frequency spike activity, such 601-1 and 603-3. Thishigh frequency spike activity is a sign of contraction by the muscle,indicating normal motility.

As seen at slow wave 602, however, no high frequency spike activity ispresent. This indicates a lack of peristaltic waves in the stomach andthus diminished motility. As discussed above, the present inventiondetects such diminished motility and delivers electrical stimulation. Inparticular, the pulse generator features two sensors. The first sensorsenses slow waves, like 601, 602 and 603. The second sensor senses spikeactivity, like 601-1 and 603-3. The pulse generator further deliversstimulation pulse trains to the gastrointestinal tract at a period oftime after slow waves have been sensed by the first sensor. If, however,the second sensor senses intrinsic spike activity between the frequencyof 100-5000 Hz, then the delivery of stimulation pulse trains to thegastrointestinal tract is inhibited. In such a manner the presentinvention provides electrical stimulation to the gastrointestinal tractat all times except when normal gastric activity is detected. At 604 theslow wave rate interval has timed out and a pulse train consisting of aslow wave escape stimulation is delivered at 605. As seen in thisillustration 605 is a pulse train with two components, a low frequencyhigh amplitude front followed by a lower amplitude higher frequency end.

FIG. 7 is a flowchart of the present invention. FIG. 7 is a flow chartof the present invention. As seen, in operation, the invention generallyrequires sensing of the two distinct waves or electrical signals in theEGG, low frequency slow waves and high frequency spike activity. Asdiscussed above, slow waves are sensed in the frequency range ofapproximately 0.005-5 Hz while spike activity is sensed in the range ofapproximately 100-5000 Hz. At step 7-1 slow waves are sensed. If no slowwaves are sensed then the device proceeds to step 7-2 with the lowerrate timer operating. As seen, if the lower rate limit timer is nottimed out, then the device resets and continues looping between step 7-1and step 7-2. If the lower rate timer is timed out then the deviceproceeds to step 7-4 and delivers slow wave electrical stimulation. Asdiscussed above, slow wave electrical stimulation is delivered tonormalize the slow waves in the stomach which have been found to be aneffective treatment for the symptoms of gastroparesis, e.g. nausea orvomiting. Slow wave electrical stimulation may comprise either a singlepulse or a series of pulses delivered at a frequency of 10-100 Hz havingan amplitude of 3 V and a pulse width of 330 ms. If a low frequency slowwave is sensed at step 7-1, however, then the device proceeds todetermine whether any spike activity is sensed. Once the slow waveelectrical stimulation is delivered the device proceeds to step 7-5 anddelivers burst electrical stimulation. The burst electrical stimulationis delivered at step 7-5 in order to elicit or cause a contraction ofthe stomach. If spike activity is sensed, then the device proceeds tostep 7-6, and determines whether the number of spikes is lower than aselected value. If the number of spikes is lower than the selectedvalue, then an adequate contraction of the stomach is deemed not to haveoccurred and the device proceeds to step 7-5 where it delivers burstelectrical stimulation to thereby cause a contraction of the stomach.If, however, sufficient number of spikes are sensed in step 7-6, thenthe device is reset and proceeds again through the loop beginning atstep 7-1. Through this algorithm it is thus seen that the devicecontinuously monitors first, whether slow waves occur in the stomachand, if they are not occurring, delivers slow wave electricalstimulation followed by burst electrical stimulation. If, however, slowwaves are sensed then the device determines whether or not spikeactivity is following. If an insufficient amount of spike activity isfollowing then burst electrical stimulation is delivered to therebycause a contraction. If sufficient high frequency spike activity isoccurring then the device resets itself and again senses for slow waves.For example, as discussed above, the device may be programmed to detectspike activity and count the number of spikes sensed associated to eachcorresponding slow wave. This number of spikes corresponding to eachslow wave and thus each contraction may be counted and tallied todetermine or assess the strength of the contractions. In the preferredembodiment 3-5 spikes correspond to a weak contraction; 6-8 spikescorrespond to a moderate contraction and 9 or more spikes correspond toa strong contraction. Each of these values, of course, may be programmedand the exact number of spikes necessary to achieve the correspondingcharacterization of the contraction will vary due to the organ in whichthe device is used.

FIG. 8a depicts a pulse train used in the present invention. As seen,the preferred pulse train 300 is emitted at a frequency of 30 Hz and hasa duration of approximately 4 seconds, each pulse lasting 330microseconds with an amplitude of 0.5 to 10 Volts or a current ofbetween approximately 0.1 milliamps to 30 milliamps. In an alternativeembodiment all of the stimulation may be programmed as well as thewaveforms used and their phase.

FIG. 8b depicts an alternate pulse train which may be used with thepresent system. Muscle stimulation burst 300 has essentially twosections, first section 301 and second section 302. As seen, firstsection 301 has a smaller interpulse interval 304 within the burst, i.e.a higher frequency. In comparison second section 302 has a relativelylarger interpulse interval 304 within the burst, i.e. a relativelysmaller frequency. In the preferred embodiment interpulse interval 304and number of pulses in the first section may be selected by thephysician. The pulse waveform and amplitude 308 are the same for theremainder of the burst.

FIG. 8c depicts an alternate embodiment of a pulse train which may beused with the present system. As seen all parameters of the musclestimulation burst 300 are the same as that described above with respectto FIG. 8a but for the amplitude of second section 302.

FIG. 8d depicts an alternate embodiment of a pulse train which may beused with the present system. As seen all parameters of the musclestimulation burst 300 are the same as that described above with respectto FIG. 7 but for the amplitude of second section 302. In particularamplitude of each burst within second section 302 decreases.

FIG. 8e depicts an alternate embodiment of a pulse train which may beused with the present system. As seen burst 300 consists of a number ofpulses 309. The amplitude of each pulse 309 differs from the amplitudeof each preceding and following pulse. In addition, the interpulseinterval between each pulse 309 is different. None of 320, 321, 322,323, 324, 325 or 326 are equal to another. Each of the variousparameters, such as amplitude 308 and the rate of change of amplitude308, synchronization delay 305 and interpulse intervals 320, 321, 322,323, 324, 325 and 326 are programmed on a patient by patient basis so asto attain the most efficient stimulation while minimizing energyexpenditure. Of course other unique waveforms of pulse trains may alsobe used, such as biphasic or poly phasic for example. In addition eachof the above identified various parameters, including frequency,amplitude, rate of change of amplitude, rate of change of interpulseinterval, etc. may be programmed on a patient by patient basis so as toattain the most efficient stimulation while minimizing energyexpenditure.

From a system component viewpoint the system operates as follows. Uponthe detection of a sensed slow wave or a principal stimulated event, theescape timer is reset and starts counting. A stimulation pulse or pulsetrain will be emitted at the end of the timing out of the escape timer.If however, a slow wave is detected after the end of the refractoryperiod and before the escape interval times out, then the stimulation isinhibited and the counters are reset. This occurs in the inhibited mode,similar to VVI cardiac pacing. If, however, ratio escape interval to astimulation interval is programmed, e.g., a value of 5 and the escapeinterval is 20 seconds, then stimulation pulses would be emitted every 4seconds but stimulation during the refractory period will not reset theescape timer.

If a contraction occurs, spike activity is seen in theelectrogastrogram. To avoid saturation of the slow wave detectioncircuit 41 of spike activity, the amplifier is connected via a switch tothe connecting electrodes. This switch connects the amplifier to thesensing electrodes once an intrinsic deflection has been detected or astimulus has been emitted. This could occur after a short delay. Theswitch is closed roughly 0.5-2 seconds after the above events, andcloses roughly 5-7 seconds later or at 30% of the intrinsic interval.The switch is controlled via the line 46e-42e from the microprocessor46. Each confirmation of a detected spike and the interval between twodetections is stored in the memory of the microprocessor 46. When theblanking switch is opened, the microprocessor 46 calculates the numberof spikes sensed. If the number of spikes sensed is above a set level,for example, 7, and if the interval between the spikes does notcorrespond to the interval of the main frequency or multiples from it,then the microprocessor 46 confirms a mechanical contraction has beensensed. This event, with its time of occurrence, is stored in memory.

Another method which may be used to detect mechanical contractions ofthe underlying tissue is plethysmorgraphy. Plethysmorgraphy may be usedto validate the high frequency spike activity detection or programmed onif the electrodes are at locations where no high frequency spikeactivity may be sensed. The operation of the plethysmorgraphy circuit isas follows. The current generator injects an AC current between 100microamps and 10 milliamps at a frequency of 1 kilohertz to 20 kilohertzbetween the two sensing electrodes or a sensing electrode and theimplantable pulse generator can, as is well known in the art. Thecurrent generator is switched on a few seconds (1-3 seconds) after thedetection of a slow wave or after the emission of a principle stimulus.The current generator is then switched off roughly 7 to 10 seconds laterafter the detected event. The amplifier could have a front end switch toavoid saturation by stimulation or the slow wave. The operation of theswitch and timing is identical to that discussed above with regards tothe blanking switch, but the total interval the switch is left open islonger, 7-10 seconds, due to the electrical mechanical delay of theunderlying tissue. In case of sampling the impedance wave form, it couldbe made to be either synchronous or asynchronous to the AC currentsource.

The sequential digitized signals sensed using the sensing electrodes arecompared with templates collected and stored in the microprocessor 46.In the preferred embodiment, the templates are collected during themigrating motor complex phase at which no spike activity is detected.Such a phase is created during a learning period of the pulse generatorso that the templates may be collected and stored. The migrating motorcomplex phase includes postural changes, coughing and perhaps evenhurling. The learning period of the pulse generator should also includeperiods when the patient is prandal and when spike activity is detected.A template corresponding or useful to identifying vomiting may becollected as follows. If the amplitude of the measured signal exceedsthe highest value during the migrating motor complex phase of thelearning period of the pulse generator and no vomiting occurred duringthat time, then the sensed signal should be concluded as being orcorresponding to vomiting

FIG. 9 depicts the specific steps used in the present invention todetermine contraction or vomiting or other changes in the stomach usingplethysmography. At 9-1 the voltage resulting from the injection of ACcurrent is sampled. At 9-2 the AC voltage profile is generated overtime. At 9-3 the generated AC voltage profile is compared to storedtemplates to reach a probable diagnosis. Examples of such storedtemplates are further shown, e.g. the change in AC voltage due to anormal contraction, vomiting or a postural change. At 9-4 the probablediagnosis is compared against whether any spike activity is detected. At9-5 an output of whether the diagnosis is confirmed is provided.

At each stimulus emitted or every preset numbers of stimuli, theelectrode tissue impedance is measured. Such a scheme is well known inthe art as seen in the Medtronic Itrel III Nerve Stimulator. If theelectrode tissue impedance increases significantly between twomeasurements or if the electrode tissue impedance exceeds a presetlevel, then one may conclude the stimulation will be ineffective and anelectrode may be dislodged. From that time forward the stimulator isswitched to an off position so that no output signals are sent.

FIG. 10 depicts the electrical stimulation delivered in the normal modeof the device. Electrical stimulation preferably consists of a pulsetrain delivered at a rate of between 7-27 bpm with 12 bpm preferred. Asseen, the pulse train preferred consists of two pulses, the pulse havingan amplitude A, a pulsewidth PW and an inter pulse interval II. II maybe anywhere between 6-600 ms in length with 60 ms preferred, A isbetween 1-50 milliamps with 5 milliamps preferred and pulsewidth isbetween 3-1000 microsecs with 330 microsecs preferred. Moreover,although the pulse train consisting of two pulses is preferred, anynumber of pulses between 1-100 may be used. As discussed above, theexact parameters selected depend not only on the organ to be stimulatedbut also upon the patient's physiology as well as on the preference ofthe physician attending.

While the present invention has been described in detail with particularreference to a preferred embodiment, it will be understood variationsand modifications can be effected within the scope of the followingclaims. Such modifications may include substituting elements orcomponents which perform substantially the same function insubstantially the same way to achieve substantially the same result forthose described herein.

What is claimed is:
 1. An apparatus for providing electrical stimulationto the gastrointestinal tract comprising:a medical electrical leadhaving means for electrically coupling to the gastrointestinal tract; afirst sensor for sensing intrinsic gastrointestinal electrical activitybetween the frequency of 100-5000 Hz, the sensor coupled to the meansfor electrically coupling to the gastrointestinal tract, the sensoremitting an intrinsic gastrointestinal electrical activity signal uponthe sensing of intrinsic gastrointestinal electrical activity; a pulsegenerator coupled to the medical electrical lead having means forelectrically coupling to the gastrointestinal tract and the firstsensor, the pulse generator emitting asynchronous stimulation pulsetrains at a first rate, the pulse generator inhibiting the emission ofasynchronous stimulation pulse trains at a first rate upon the emissionof the intrinsic gastrointestinal electrical activity signal by thefirst sensor.
 2. The apparatus according to claim 1 wherein thestimulation pulse trains comprise a series of pulse trains emitted at afrequency of 30 Hz and a duration of approximately 4 seconds, each pulselasting 330 microseconds with an amplitude of between approximately 0.5to 10 Volts or a current of between approximately 0.1 milliamps to 30milliamps.
 3. The apparatus according to claim 1 wherein the pulse trainhaving a first section and a second section, the first section having afirst frequency, the second section having a second frequency.
 4. Theapparatus of claim 3 wherein the first frequency is greater than thesecond frequency.
 5. The apparatus of claim 3 wherein the firstfrequency is less than the second frequency.
 6. The apparatus of claim 3wherein the first section has a first amplitude, the second section hasa second amplitude.
 7. The apparatus of claim 3 wherein the firstamplitude is less than the second amplitude.
 8. An apparatus forproviding electrical stimulation to the gastrointestinal tractcomprising:a medical electrical lead having means for electricallycoupling to the gastrointestinal tract; a first sensor for sensing lowfrequency gastrointestinal electrical activity between the frequency of0.017-0.25 Hz, the sensor coupled to the means for electrically couplingto the gastrointestinal tract, the sensor emitting a low frequencygastrointestinal electrical activity signal upon the sensing of lowfrequency gastrointestinal electrical activity; a second sensor forsensing intrinsic gastrointestinal electrical activity between thefrequency of 100-5000 Hz, the sensor coupled to the means forelectrically coupling to the gastrointestinal tract and the firstsensor, the second sensor emitting an intrinsic gastrointestinalelectrical activity signal upon the sensing of intrinsicgastrointestinal electrical activity between the frequency of 100-5000Hz within a pre-set period after the emission of a low frequencygastrointestinal electrical activity signal by the first sensor; a pulsegenerator coupled to the means for electrically coupling to thegastrointestinal tract, the first sensor and the second sensor, thepulse generator emitting asynchronous stimulation pulse trains at afirst rate, the pulse generator inhibiting the emission of asynchronousstimulation pulse trains at a first rate upon the emission of theintrinsic gastrointestinal electrical activity signal by the secondsensor.
 9. A method of electrically stimulating an organ of thegastrointestinal tract comprising the steps of:sensing low frequencyslow waves within an organ of the gastrointestinal tract; determiningwhether the sensed low frequency slow waves a exceeds predetermined slowwave amount; delivering slow wave electrical stimulation if the sensedlow frequency slow waves do not exceed the predetermined slow waveamount and delivering burst electrical stimulation; sensing highfrequency spike activity within the organ of the gastrointestinal tract;determining whether the sensed high frequency spike activity exceeds apredetermined fast wave amount; and delivering burst electricalstimulation if the sensed high frequency spike activity is lower thanthe predetermined fast wave amount.
 10. The method of electricallystimulating an organ of claim 9 wherein the step of sensing lowfrequency slow waves comprises sensing gastrointestinal electricalactivity between the frequency of approximately 0.017-0.25 Hz.
 11. Themethod of electrically stimulating an organ of claim 9 wherein the stepof sensing high frequency spike activity comprises sensinggastrointestinal electrical activity between the frequency ofapproximately 100-5000 Hz.
 12. The method of electrically stimulating anorgan of claim 9 wherein the step of sensing high frequency spikeactivity comprises sensing gastrointestinal electrical activity betweenthe frequency of approximately 100-5000 Hz for only a preset period oftime after the step of sensing low frequency slow waves.
 13. The methodof electrically stimulating an organ of claim 9 wherein the step ofdelivering slow wave electrical stimulation comprises a series of pulsetrains emitted at a frequency of 30 Hz and a duration of approximately 4seconds, each pulse lasting 330 microseconds with an amplitude ofbetween approximately 0.5 to 10 Volts or a current of betweenapproximately 0.1 milliamps to 30 milliamps.
 14. The method ofelectrically stimulating an organ of claim 9 wherein the step ofdelivering burst electrical stimulation comprises delivering a series ofpulse trains emitted at a frequency of 30 Hz and a duration ofapproximately 4 seconds, each pulse lasting 330 microseconds with anamplitude of between approximately 0.5 to 10 Volts or a current ofbetween approximately 0.1 milliamps to 30 milliamps.
 15. A method ofelectrically stimulating an organ comprising the steps of:sensing aparameter indicative of the fullness of an organ within the GI tract;sensing the absence of muscular contractions in the organ; anddelivering an electrical muscular contraction stimulation to the organto thereby cause a contraction to occur in the organ.
 16. The method ofelectrically stimulating an organ of claim 15 wherein the step ofsensing the absence of muscular contractions in the organcomprises:sensing low frequency slow waves; and sensing gastrointestinalelectrical activity between the frequency of approximately 100-5000 Hzfor only a preset period of time after the step of sensing low frequencyslow waves.
 17. An apparatus for providing electrical stimulation to thegastrointestinal tract comprising:a pulse generator, the pulse generatorgenerating electrical stimulation pulse trains at a pre set frequency, amedical electrical lead having means for electrically coupling to thegastrointestinal tract; means for sensing low frequency slow waveswithin an organ of the gastrointestinal tract; and means for sensinghigh frequency spike activity within an organ of the gastrointestinaltract for a first pre set period of time after the sensing of lowfrequency slow waves, the means for sensing high frequency spikeactivity coupled to the pulse generator and inhibiting the generation ofthe electrical stimulation pulse trains for a second pre set period oftime when the sensed high frequency spike activity exceeds a programmedhigh frequency spike activity value.
 18. The apparatus of claim 17wherein the means for sensing low frequency slow waves comprises meansfor sensing gastrointestinal electrical activity between the frequencyof approximately 0.017-0.25 Hz.
 19. The apparatus of claim 17 whereinthe means for sensing high frequency spike activity for a first pre setperiod of time after the sensing of low frequency slow waves comprisesmeans for sensing gastrointestinal electrical activity between thefrequency of approximately 100-5000 Hz.